Message-ID: <20141104163845.GA369@kroah.com>
Date:	Tue, 4 Nov 2014 08:38:45 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Thierry Reding <thierry.reding@...il.com>
Cc:	Daniel Vetter <daniel.vetter@...ll.ch>,
	David Herrmann <dh.herrmann@...il.com>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 1/2] core: Add generic object registry implementation

On Tue, Nov 04, 2014 at 05:29:27PM +0100, Thierry Reding wrote:
> From: Thierry Reding <treding@...dia.com>
> 
> Add a generic implementation of an object registry. This targets drivers
> and subsystems that provide auxiliary objects that other drivers need to
> look up. The goal is to put the difficult parts (keep object references,
> module usage count, ...) into core code so that individual subsystems do
> not have to deal with them.
> 
> The intention is for subsystems to instantiate a struct registry and use
> a struct registry_record embedded into a subsystem-specific structure to
> provide a subsystem-specific API around that.
> 
> Signed-off-by: Thierry Reding <treding@...dia.com>
> ---
>  drivers/base/Makefile    |   2 +-
>  drivers/base/registry.c  | 147 +++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/registry.h |  62 ++++++++++++++++++++
>  3 files changed, 210 insertions(+), 1 deletion(-)
>  create mode 100644 drivers/base/registry.c
>  create mode 100644 include/linux/registry.h
> 
> diff --git a/drivers/base/Makefile b/drivers/base/Makefile
> index 53c3fe1aeb29..250262d1af2c 100644
> --- a/drivers/base/Makefile
> +++ b/drivers/base/Makefile
> @@ -4,7 +4,7 @@ obj-y			:= component.o core.o bus.o dd.o syscore.o \
>  			   driver.o class.o platform.o \
>  			   cpu.o firmware.o init.o map.o devres.o \
>  			   attribute_container.o transport_class.o \
> -			   topology.o container.o property.o
> +			   topology.o container.o property.o registry.o
>  obj-$(CONFIG_DEVTMPFS)	+= devtmpfs.o
>  obj-$(CONFIG_DMA_CMA) += dma-contiguous.o
>  obj-y			+= power/
> diff --git a/drivers/base/registry.c b/drivers/base/registry.c
> new file mode 100644
> index 000000000000..9f510f6237b7
> --- /dev/null
> +++ b/drivers/base/registry.c
> @@ -0,0 +1,147 @@
> +/*
> + * Copyright (C) 2014, NVIDIA Corporation.  All rights reserved.
> + *
> + * This file is released under the GPL v2.
> + */
> +
> +#include <linux/device.h>
> +#include <linux/module.h>
> +#include <linux/registry.h>
> +
> +static inline struct registry_record *to_registry_record(struct kref *kref)
> +{
> +	return container_of(kref, struct registry_record, kref);
> +}
> +
> +static void registry_record_release(struct kref *kref)
> +{
> +	struct registry_record *record = to_registry_record(kref);
> +
> +	record->release(record);
> +}
> +
> +/**
> + * registry_record_init - initialize a registry record
> + * @record: record to initialize
> + *
> + * Sets up internal fields of the registry record so that it can subsequently
> + * be added to a registry.
> + */
> +void registry_record_init(struct registry_record *record)
> +{
> +	INIT_LIST_HEAD(&record->list);
> +	kref_init(&record->kref);
> +}
> +
> +/**
> + * registry_record_ref - reference on the registry record
> + * @record: record to reference
> + *
> + * Increases the reference count on the record and returns a pointer to it.
> + *
> + * Return: A pointer to the record on success or NULL on failure.
> + */
> +struct registry_record *registry_record_ref(struct registry_record *record)
> +{
> +	if (!record)
> +		return NULL;
> +
> +	/*
> +	 * Refuse to give out any more references if the module owning the
> +	 * record is being removed.
> +	 */
> +	if (!try_module_get(record->owner))
> +		return NULL;
> +
> +	kref_get(&record->kref);

You "protect" from a module being removed, but not from someone else
releasing the kref at the same time.  Where is the lock that prevents
this from happening?

And do we really care about module reference counts here?

> +
> +	return record;
> +}
> +
> +/**
> + * registry_record_unref - drop a reference to a registry record
> + * @record: record to unreference
> + *
> + * Decreases the reference count on the record. When the reference count
> + * reaches zero the record will be destroyed.
> + */
> +void registry_record_unref(struct registry_record *record)
> +{
> +	if (record) {
> +		/*
> +		 * Keep a copy of the module owner since the record may
> +		 * disappear during the kref_put().
> +		 */
> +		struct module *owner = record->owner;
> +
> +		kref_put(&record->kref, registry_record_release);
> +		module_put(owner);
> +	}
> +}
> +
> +/**
> + * registry_add - add a record to a registry
> + * @registry: registry to add the record to
> + * @record: record to add
> + *
> + * Tries to increase the reference count of the module owning the registry. If
> + * successful adds the new record to the registry.
> + *
> + * Return: 0 on success or a negative error code on failure.
> + */
> +int registry_add(struct registry *registry, struct registry_record *record)
> +{
> +	if (!try_module_get(registry->owner))
> +		return -ENODEV;
> +
> +	mutex_lock(&registry->lock);
> +	list_add_tail(&record->list, &registry->list);
> +	mutex_unlock(&registry->lock);

No incrementing of the reference of the record at all?

You seem to be using 2 reference counts for the record / registry, a
module count, and a kref count, which can cause confusion...

thanks,

greg k-h
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